The Belgian headed home a Juan Mata cross midway through the first half to score what would prove to be the only goal of the game, but his subdued reaction to the goal provoked plenty of debate.

Lukaku did eventually raise a hand and point to the skies, but before that he bowed his head and became buried in his teammates.

Lukaku heads home what proved to be the winner (Image: PA)

But his celebration was somewhat muted (Image: Getty Images Europe)

He did eventually raise an arm in celebration (Image: Getty Images Europe)

The Belgian had been facing criticism following his reported involvement in the fracas which followed United's 2-1 defeat to neighbours Manchester City at the weekend, when City coach Mikel Arteta was left with a cut to the face.

Lukaku had also unwittingly 'assisted' both City goals at Old Trafford with his attempted clearances.

And on Twitter, plenty of fans - including Match of the Day presenter Gary Lineker - wondered if the forward was trying to make a point by not seeming too enthused by the goal.

Lukaku's place in the team has come under pressure following the return of Zlatan Ibrahimovic to the United squad, but he has still started every one of his side's Premier League games this season.